The specimen holder is a component of an electron microscope providing the physical support for specimens under observation. Specimen holders traditionally used for TEMs and STEMs, as well as some modern SEMs, consist of a rod that is comprised of three key regions: the end, the barrel and the specimen tip (see, e.g., FIG. 1). In addition to supporting the specimen, the specimen holder provides an interface between the inside of the instrument (i.e., a vacuum environment) and the outside world.
To use the specimen holder, one or more samples are first placed on a support device. The support device is then mechanically fixed in place at the specimen tip, and the specimen holder is inserted into the electron microscope through a load-lock. During insertion, the specimen holder is pushed into the electron microscope until it stops, which results in the specimen tip of the specimen holder being located in the column of the microscope. At this point, the barrel of the specimen holder bridges the space between the inside of the microscope and the outside of the load lock, and the end of the specimen holder is outside the microscope. To maintain an ultra-high vacuum environment inside the electron microscope, flexible o-rings are typically found along the barrel of the specimen holder, and these o-rings seal against the microscope when the specimen holder is inserted. The exact shape and size of the specimen holder varies with the type and manufacturer of the electron microscope, but each holder contains these three key regions.
Interfacing semiconductor-based devices with specimen holders for use in electron microscopes has seen limited commercial development. There are, however, a few applications that have either required an electrical interface between the sample and the specimen holder, or have incorporated semiconductor devices in a research environment.
Several electron microscopy techniques, including Electron Beam Induced Current (EBIC), require an electrical contact between a sample and the specimen holder itself. Typically, this is done using a simple screw and metallic clip, which is gently pressed down onto the sample by tightening the screw (see, X. Zhang and D. Joy, “A simple specimen holder for EBIC imaging on the Hitachi S800,” J. Microscopy Res. and Techn. , Vol. 26(2), pp. 182-183, 1993). A wire is either soldered to the clip or looped around the screw head to provide an electrical path from the sample, through the clip, and to the specimen holder which routes the wire outside of the instrument. This approach is tedious, requiring the user to manually align the clips over the appropriate regions on the device, then manually tighten every screw that is needed to complete an electrical path to the specimen holder. Because of the small size of these screws and the sample itself, this approach takes time and requires a substantial amount of dexterity.
An alternative approach (U.S. Pat. No. 5,124,645) requires a wirebond, or solder joint, to establish a more durable connection between the sample and the specimen tip of a specimen holder. These connections, however, are permanent and do not allow samples to be easily interchanged between experiments. Following an experiment, to exchange samples, the specimen holder must be placed back into a wirebond machine or soldering must again be performed to create a new electrical connection with the new sample. This approach is tedious, requires great dexterity, and is likely to damage the specimen tip after repeated use.
An approach developed at the University of Illinois (U.S. patent application Ser. No. 11/192,300) addresses some of these concerns. This approach allows a semiconductor device to be mounted in a specimen tip, making as many as twelve simultaneous electrical connections between the holder and the device. A frame (generally U-shaped) aligns the device and baseplate with electrical spring contact fingers and provides a rigid surface against which the device is pressed, providing stability and forming electrical contacts between the device and the specimen holder. The baseplate is the component of the specimen tip that provides a stable surface upon which the device can be mounted, and contains electrical spring contact fingers in complementary positions to the device, which when aligned using the frame, make contacts simultaneously between the baseplate and the device. Disadvantageously, spring contact fingers such as these are delicate and more difficult to manufacture. Removing the device from the baseplate completely exposes the spring clips and presents an opportunity to accidentally bend or break these fingers, compromising the electrical connections.
Considering the disadvantages of the prior art, a novel specimen holder is needed, wherein said specimen holder eliminates the need for delicate spring contact fingers and provides a simple method for repeatedly mounting and exchanging devices without disassembly or soldering.